1. Field of the Invention
The present invention relates to a sedimentation apparatus for coagulating and precipitating suspended solids or the like in a liquid to be treated within a sedimentation tank, so as to clarify the liquid.
2. Related Background Art
Coagulating sedimentation apparatus are a kind of sedimentation type water treatment apparatus, which flocculate suspended solids or the like contained in a liquid to be treated such as raw wastewater by coagulating it with an appropriate additive, thereby eliminating the suspended solids from the liquid by sedimentation operation.
As this kind of sedimentation apparatus, one disclosed in Japanese Patent Publication No. HEI 1-38523 has been known. The sedimentation apparatus described in the publication, includes a tubular mixing chamber for coagulating the suspended solids or the like by mixing the liquid to be treated with an additive. The mixing chamber is disposed in an upright state within a sedimentation tank at the center thereof. Also, a distributor is disposed at the lower end of the mixing chamber, by which the liquid to be treated having coagulated flocs is distributed into the inner space within the tank. In this specification, the inner space excludes the space within the mixing chamber, hereinafter referred to as xe2x80x9csedimentation spacexe2x80x9d.
A distributor developed in recent years is basically constituted by a cup-shaped rotary support, connected to a lower portion of a center shaft disposed within the mixing chamber concentrically therewith, functioning as a bottom of the mixing chamber; a plurality of discharge pipes radially extending from the outer peripheral surface of the rotary support; and a driving device for rotating the center shaft. When the center shaft is rotated, the floc-containing liquid to be treated is discharged from discharge orifices of the individual discharge pipes and is evenly distributed into the sedimentation space within the sedimentation tank.
In the sedimentation space, the coagulated floc in the liquid is separated by sedimentation operation and forms a concentrated sludge layer at the bottom region of the tank. On the other hand, clear supernatants ascend to the upper region of the tank, and a very clear supernatant near the liquid surface is collected by a trough disposed at the upper region of the tank and is taken out of the tank through an outlet communicating with this trough.
The above-mentioned conventional sedimentation apparatus can efficiently yield clarified supernatants and are used for various purposes, e.g., for treating wastewater, collecting papermaking white water, and so forth. However, as sedimentation apparatus of this type have come into wider use, the following problems have been noticed.
In the typical sedimentation apparatus, the liquid to be treated is continuously introduced into an upper portion of the mixing chamber through a conduit; whereas the liquid within the mixing chamber is discharged from the rotating distributor below the mixing chamber. Meanwhile, the liquid within the mixing chamber contains particles having a relatively high specific gravity, and suspended solids or the like which coagulates and forms bulky flocs within a short period of time under the action of an additive.
As a consequence, the particles and flocs may sediment within the mixing chamber to directly accumulate within the rotary support of the distributor, which functions as the bottom of the mixing chamber, before flowing into the discharge pipes from the mixing chamber. If sludge or the like accumulates within the rotary support or the bottom of the mixing chamber, the discharge pipe inlets in the distributor may be blocked. If the discharge pipe inlets are blocked, then the liquid to be treated cannot efficiently be distributed into the sedimentation space in the tank, whereby clarity of supernatants may deteriorate.
Therefore, it is an object of the present invention to provide a coagulating sedimentation apparatus having a favorable operating performance and yielding extremely clarified supernatants.
For achieving the above-mentioned object, the present invention provides a coagulating sedimentation apparatus for precipitating and separating suspended solids, coagulated flocs or the like in a liquid to be treated, so as to clarify the liquid, the sedimentation apparatus comprising: a sedimentation tank; a mixing chamber disposed in an upright state within the tank concentrically therewith, for introducing, stirring and mixing the liquid and an additive therein; a cup-shaped rotary support disposed adjacent a lower end part of the mixing chamber so as to act as a bottom of the mixing chamber, the rotary support being adapted to rotate about a center axis of the mixing chamber and having a bottom portion formed with an opening; a discharge pipe extending outward from an outer peripheral surface of the rotary support, communicating with the inside of the rotary support, and having a tubular wall provided with a discharge orifice, for distributing the liquid within the mixing chamber into a precipitation space between the tank and the mixing chamber; and a blade fixed with respect to the mixing chamber and adapted to discharge a precipitate deposited on the bottom portion of the rotary support from the opening to the outside of the rotary support.
Various liquids to be treated in the sedimentation apparatus include particles having a relatively heavy weight, and suspended solids or the like which coagulates within a short period of time under the action of an additive, thereby forming bulky flocs. As a consequence, the particles and bulky flocs or the like may separating within the mixing chamber, thereby precipitating at the bottom of the rotary support without flowing into the discharge pipe of the distributor. In view of this point, the bottom portion of the rotary support in this sedimentation apparatus is formed with an opening, whereas a scraping blade is fixed with respect to the mixing chamber.
Namely, during the operation of the sedimentation apparatus, the rotary support rotates relative to the mixing chamber, whereby the scraping blade fixed to the mixing chamber pivots with respect to the rotary support. As a consequence, the precipitate deposited on the bottom of the rotary support during the operation of the sedimentation apparatus is scraped into the opening by the scraping blade, and is discharged into the tank by way of the opening. As a result, the inlet of the discharge pipe is prevented from being blocked, so that the liquid to be treated is always efficiently distributed into the tank. Hence, the operating performance of the sedimentation apparatus improves, and the clarity of supernatants also increases.
The present invention will be more fully understood from the detailed description given hereinbelow and the attached drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.